1. Field of the Invention
The present invention relates to an organic semiconductor material and an organic thin-film transistor.
2. Description of the Related Art
Recently, organic thin-film transistors (hereinafter referred to as organic TFTs, as the case may be) have made great progress. Organic materials are superior in workability to inorganic materials, and hence there is a possibility that use of organic materials enables to realize low-cost devices. As has been recently reported, even when organic semiconductor materials are used, performances such as field-effect mobility are comparable with those obtained by using amorphous silicon TFTs, and organic thin-film transistors are expected to be put into practical use as transistors to drive displays or the like (see, for example, IEEE Electron Device Lett., 44, p. 1325, 1997). However, organic materials suffer from problems such that organic materials are inferior in storage stability to inorganic materials. Accordingly, new organic semiconductor materials have been demanded.
It has been known that for the purpose of improving the storage stability of an organic semiconductor material, it is effective to lower the HOMO (highest occupied molecular orbital) of the organic semiconductor material (see, for example, J. Am. Chem. Soc., 126, p. 3378, 2004). Examples of recently developed organic semiconductor materials include thiophene-phenylene oligomer and thiophene-thiazole oligomer (see, for example, Chem. Mater., 13, p. 4686, 2001), and further include a compound in which two molecules of thiophene are bonded to anthracene (see, for example, J. Am. Chem. Soc., 127, pp. 2406-2407, 2005) and an anthracene oligomer (see, for example, Japanese Patent Application Laid-Open No. 2004-107257).
However, when the HOMO is lowered largely as reported in J. Am. Chem. Soc., 126, p. 3378, 2004, the charge transport performance is also degraded, and accordingly, it is extremely difficult to make high ON current and excellent storage stability compatible with each other.
Additionally, the organic semiconductor materials reported in Chem. Mater., 13, p. 4686, 2001, J. Am. Chem. Soc., 127, pp. 2406-2407, 2005, Japanese Patent Application Laid-Open No. 2004-107257 and others each have relatively high ON current and relatively excellent storage stability, but such ON current and such storage stability are not sufficient for practical applications.